The present invention relates to an automotive seat reclining device having a pair of wedge members to hold a seat back tightly at a desired angular position relative to a seat cushion without causing play in the seat back due to tilting of the wedge members.
Japanese Laid-Open Patent Publication No. 2004-33401 discloses an automotive seat reclining device that has a seat back angle adjustment mechanism equipped with a differential gear unit to pivot a seat back electrically at a high reduction gear ratio and thereby adjust the seat back to a desired angular position with respect to a seat cushion.
The differential gear unit generally includes a first rotation member (or bracket) coupled to either one of the seat cushion and the seat back and formed with an internal gear and a bearing sleeve, a second rotation member (or bracket) coupled to the other of the seat cushion and the seat back and formed with an external gear and a bearing bore, a pair of wedge members disposed within a circular eccentric space between an outer circumferential surface of the bearing sleeve and an inner circumferential surface of the bearing bore and biased away from each other by a spring and a drive member inserted in the eccentric space to move the mesh of the internal and external gears circumferentially together with the wedge members and thereby rotate the second rotation member relative to the first rotation member in a direction opposite to the rotation direction of the gear mesh. Each of the wedge members has an inner circumferential surface formed with a protrusion for sliding line contact with the outer circumferential surface of the bearing sleeve.